A substantial portion of costs associated with the maintenance of commercial and residential buildings is attributable to energy consumption, including heating and cooling. Windows are the single largest point source of energy loss in a building envelope. Many U.S. buildings do not possess energy efficient windows that meet current standards and, generally, the only practical means to address these energy losses was to replace the existing windows with modern replacement windows such as 2 or 3-pane systems that can reduce energy losses through the window units. Commercially available “high performance” replacement windows, if installed correctly, can deliver substantial improvements in energy savings if replacing either a single pane or double pane window.
However, full window replacement is costly due to the high cost of the new window, installation and disposal fees, site preparation and finishing, and possible remediation (all buildings constructed before 1978 pose the risk of exposing occupants to lead contamination when the building envelope is disrupted). Hence, due to these high costs, full window replacement is rarely, if ever, economically justified solely on the basis of energy savings or consequent improvements in occupant comfort. For this reason, traditional weatherization efforts, despite recognizing the energy loss associated with a building's windows, have elected not to address window energy losses beyond minimal caulking and weatherstripping, despite their substantially adverse impact on building operating costs, occupant comfort, and environmental considerations.
Weatherization programs that measure before and after energy consumption have historically shown a rather consistent pattern where 10-30 percent of the homes which are weatherized show no improvement in energy consumption, and in some cases, an increase in energy consumption after being weatherized. While the specific causes of this phenomena are not fully understood, it does account for a decrease in the overall cost effectiveness of building weatherization. There is some empirical evidence suggesting that windows, which are known to be a source of occupant discomfort due to mean radiant temperature effects and natural convection drafts, if not properly addressed as an element of a weatherization project, may be the cause of the problem as each of these window-related consequences would cause a home owner to adjust the interior room temperature (calling for increased heat) seeking to offset the discomfort associated with poor window performance.
For at least these reasons, there remains a need for improved window systems that can reduce energy consumption and enhance occupant comfort in commercial and residential buildings.